Associated with downsizing, lightening, and functionalization of electronic devices, packaging of a semiconductor device is mainly performed by surface mounting method rather than pin insertion method. Recently, the system-in-packaging, hereinafter referred to as SIP, is widely used in which a plurality of silicon dies is packaged in one package. Particularly, a stack type SIP is used in which at least one semiconductor chip is stacked and wire bonded on another semiconductor chip.
FIG. 1 is a cross-sectional view of a semiconductor device, in which a semiconductor chip 3 is flip-chip bonded via solder bumps 2 on a surface of a substrate 1 provided with electronic circuits. The gaps between the substrate 1 and the semiconductor chip 3, i.e., spaces between the solder bumps, are filled with an underfill composition 4. FIGS. 2 and 3 show cross-sectional views of system-in-package type semiconductor devices in which one or more of semiconductor chip is placed via a die attach layer 5 on a semiconductor chip flip-chip bonded to the substrate 1. The reference numerals in the drawings refer to the following features: 1=substrate; 2=solder bumps; 3=semiconductor chip; 4=underfill part; 5=die attach part; and 6=resin encapsulation part.
SIP semiconductor devices are required to show no peeling or crack at an interface between an underfill part and a silicon chip or a substrate during a reflow process and a mounting process. In addition, the underfill part must supplement weaker adhesion of a lead-free solder than that of conventional solder.
As resin materials to avoid such peeling or crack, the Japanese Patent Application Laid-Open No. H9-176287 and H9-176294 describe resin compositions comprising a liquid epoxy resin and an alkyl-substituted aromatic amine. It is described that these compositions form cured products strongly adhered to a substrate, metal and solder resist, and give a highly reliable semiconductor package having high reflow- and thermal cycle-resistances. However, when the cured products of these resin compositions are encapsulated with a resin, they were found to crack or peel depending on the encapsulation resin used.